Re: Calculation of Unbalanced 3 Phase Power?

05/22/2010 5:20 AM

Do you want to know the power consumed for a particular period?...Get the help of reading from energymeter. If you want to know the total load of each office, then calculate each circuit load and add . Is it the current reading you mentioned is full load condition? I beleive the readings are given for one phase of 3 offices.( or 3 phases of 1 office?)

Dont you have any load schedule for the distribution board?... What is the utilization factor and demand load of each distribution board?

Re: Calculation of Unbalanced 3 Phase Power?

05/22/2010 10:34 AM

You have to collect maximum demands of all offices in your commercial building. You must have a clear idea about the max. load of all offices when all loads are ON. If you have three offices which are being fed by three different phases then you can get the max. loads on each phase. Same time you collect the energy meter readings of each offices in Kwh and divide the value by 24x30 hours to get the average load per day in each phase.

Re: Calculation of Unbalanced 3 Phase Power?

05/23/2010 1:16 AM

In basic load calculation during the erection of the building first get the maximum demand load to determine your main MDB size. Distribute your circuits closely balance to each phases or per leg relevant to the rating of your PB main circuit breaker. It is not the supply voltage to be balanced but the current load of each phase. In voltage meter reading you can notice 1 or 2 volt or more difference between the phases... why? because the current load in any particular phase varries... as the current load increases the voltage drop will generates within the circuit especially when the wires or cables is not properly size relevant to the max. full load amps and length of wires to the farthest point of the circuit. Notice that in your given data 24A 29A 14. Phase L1L3 = 41.67%; L1L2 = 17.24% , L2L3 = 51.72% phase current load difference. At least not more than at max. of 33% per phase.

__________________
If there is a will... there is a way... No pain / No gain.

Re: Calculation of Unbalanced 3 Phase Power?

05/23/2010 1:42 AM

Get a class 1 power meter that connects with clamp on CTs and get a real reading over a weeks time - then move to the next office. Most of the suggestions are only going to give you a swag. The name plate power requirements for many pieces of equipment are very different from actual - could be either way, higher or lower.

Re: Calculation of Unbalanced 3 Phase Power?

Re: Calculation of Unbalanced 3 Phase Power?

05/23/2010 1:21 PM

I am not the original replyer, however the answer makes sense. When have 3 phase balanced load, you can use (sqr.3 x IL x V LL x Pf). If you do not have a balanced load you use: (V Phase X IL x pf), you do not multiply by sqr 3. However assuming a Y connected load to get the Vphase you will divide VL by Sqr 3.

Eg. If you have a balance load of 3 phase, 10A, VL = 208

Then P=sqr3 x 10 x 208 = 3600W

If you have a balance unbalanced load of 3 phase 10A, 8A, 6A, VL = 208

Re: Calculation of Unbalanced 3 Phase Power?

05/23/2010 3:29 PM

The reply by Guest in #7 will help you and is correct for each office circuit. But this is the load at the time of measurement and should be monitored for some time or for several intervals and then averaged for a period of time covering the office hours...You must monitor to find the peak load for each...

For a better measurement is to use an energy meterto record the total energy consumed for a period of time and deduct an average. But you should also consider the peak value for each circuit (This was suggested before).